Little is known about either the structure or the role of proteoglycans in fibrous extracellular matrices. Experiments are proposed to study the proteoglycan constituents in the extracellular matrix of a normal dense connective tissue, tendon and the modulation in both amounts and types of proteoglycan that occurs when tendon is subjected to altered mechanical forces. Explants of tendon in culture will be used to determine the synthetic and turnover characteristics of newly synthesized proteoglycans in each region of tendon. Cell cultures will be initiated from each region and the amounts and chemical characteristics of proteoglycans and collagen synthesized by each will be determined. These studies will define the cellular metabolism of matrix macromolecules in the system. In addition, the role of proteoglycans in determining the structural and material properties of tendon will be investigated by 1) ultra- structural study of the matrix produced by tendon fibroblast cultures to which proteoglycans known to inhibit fibrillogenesis in vitro have been added, 2) in vitro analysis of proteoglycan binding to collagen, and 3) changes in the material properties of tendon related to removal of proteoglycans from the tissue by enzymatic digestion. Finally, the expression of proteoglycan synthesis by fetal and adult cells will be modulated by subjecting cells in culture to different mechanical stresses. Restoration of function to a damaged tendon is a difficult medical problem. Investigation of the capabilities of tendon fibroblasts to produce proteoglycans and the function role of these macromolecules for matrix properties is thus relevant to both basic cell and tissue biology and also to applications in surgical procedures and tissue regeneration.